KR20000058210A - Illumination system with field mirrors for producing uniform scanning energy - Google Patents

Abstract

PURPOSE: An illuminating apparatus having a field mirror generating uniform scanning energy is provided to form a field mirror or a field lens in the illuminating apparatus. CONSTITUTION: An illuminating apparatus having a field mirror generating uniform scanning energy includes at least one field mirrors(24,25) and one field lens(24,25,33,34). The illuminating apparatus according to the present invention is used for slit illumination for scanning lithography having a wavelength less than 193nm. The field mirror(s) or the field lens(es) are formed so as for a field illuminated (41) is aberrated at a surface perpendicular to a scanning direction. The field mirror(s) or the field lens(es) are further formed so as to make the illumination variation uniform. The illumination according to the present invention is varied along with the direction perpendicular to the scanning direction. The illumination is decreased from the center of the field to the edge of the field.

Description

ILLUMINATION SYSTEM WITH FIELD MIRRORS FOR PRODUCING UNIFORM SCANNING ENERGY}

FIELD OF THE INVENTION The present invention relates to an irradiation system, in particular an illumination system for lithography consisting of a light source, at least one field mirror or one field lens and an EUV projection exposure system, having a wavelength from 193 nm to Extreme Ultra Violet (EUV), and A method for correcting scanning energy in an EUV projection exposure system.

In order to be able to reduce the structural width of the electronic components, especially in the submicron range, it is necessary to reduce the light wavelength used in microlithography. For example, lithography with weak x-ray transmission can be thought of as a wavelength smaller than 193 nm. US-A 5,339,346 discloses an arrangement for exposing a wafer with such radiation. An irradiation system for weak x-ray transmission, which is so-called EUV radiation, is shown in US-A 5,737,137, in which irradiation of a mask or reticle to be exposed is generated using three spherical mirrors.

A field mirror is shown in US Pat. No. 5,142,561, which shows good uniformity of exposure beam generation at the wafer in the lithography system. Of course, the exposure system described there relates to the contact exposure of the wafer through a mask with a high energy x-ray of 800 to 1800 eV, the irradiation system being different from the present invention.

EUV irradiation systems for EUV sources are disclosed in EP 99 106 348.8 (US series no. 09/305017) or PCT / EP99 / 02999.

A survey system with the comprehensive features of claim 1 is known as a survey system that satisfies this requirement in a unique manner.

Scanning uniformity is a problem of the scanning exposure system described above in irradiation slits, in particular curved slits. For example, the scanning energy obtained as a linear integration of the illuminance distribution along the reticle or wiper in-plane scan path increases toward the field edge despite homogeneous irradiation roughness because of the longer scan path at the field edge for the curved slit. Can be. However, the scanning energy and the scanning uniformity having it can also be affected by other influences, for example a coating or vignetting effect is possible. Curved slit typically refers to a portion of a ring field called an arc shaped field. The arc-shaped field may be represented by a width Δr, an average radius R ₀ and an angle range 2 · α. For example, the increase in scanning energy for a typical arc-shaped field with an average radius R = 100 mm and an angle range of 2 · α = 60 ° is 15%.

Accordingly, it is an object of the present invention to describe an irradiation system for a projection exposure system in which the scanning energy is uniform or can be controlled to fit a given curve.

According to the present invention, the problem is solved by shaping the field mirror (s) or field lens (s) in a comprehensive type of illumination system, causing the irradiated field to be aberration in the image plane of the illumination system perpendicular to the scanning direction. In this plane, the mask or reticle of the projection exposure system is located.

Optical components adjacent to the image plane of the illumination system mean field mirror (s) and field lens (s). In the description below, the generic word "field lens" describes field mirror (s) and field lens (s). For the wavelength λ to be higher than 100 nm, the field lens consists of refractive field lens (s), and for the wavelength in the EUV region (10 nm <λ <20 nm), the field lens consists of refractive field mirror (s). .

According to the present invention, the aberration can be determined in order to obtain a predetermined illuminance distribution.

For a scanning system, it is advantageous to have the possibility to modify the roughness distribution perpendicular to the scanning direction to obtain a uniform distribution of scanning energy in the wafer plane. Scanning energy can be affected by changing the length of the scanning path or by modifying the distribution of illumination intensity. This invention relates to the correction of distribution of illumination intensity. In contrast to a stepper system in which the two-dimensional illuminance distribution is corrected, it is sufficient for the scanner system to only correct the distribution of scanning energy.

In an advantageous embodiment of the invention, it is to provide a decreasing illumination roughness from the center of the field to the field edge portion by increasing aberrations. The illuminance is maximum at the field center (α = 0 _° ) and minimum at the field edge (α = ± α ₀ ). By reducing the illumination intensity toward the field edges, the increase in the scan path can be compensated for.

It also provides increasing irradiance from the center of the field to the field edges by decreasing aberrations. This correction is necessary if other similar layer or vignetting effects that affect reduce the scanning energy towards the field edges.

Particular preference is given to designing the field lens such that the uniformity of the scanning energy in the range of ± 7%, preferably ± 5% and very preferably ± 3% is achieved in the image plane of the irradiation system.

The field lens is shaped such that the aperture stop plane of the irradiation system is imaged with a given exit pupil of the irradiation system. Thus, field lenses achieve corrected pupil imaging in addition to illuminance correction. The exit pupil of the irradiation system is typically given by the entrance pupil of the projection. For projections having an inward pupil of the homocentric, the position of the inlet pupil is a field dependent variable. This means that the position of the exit pupil of the irradiation system is also a field dependent variable in this case.

The shape of the irradiated field according to the invention is rectangular or part of a ring field. In an advantageous embodiment of the invention, the field lens is shaped to achieve a given shape of the irradiated field. If the irradiated field is bound to a segment of the ring field, the design of the field lens determines the average radius R ₀ of the ring field.

It is advantageous to use field lenses with distortion power. This can be realized with a toroidal mirror or lens. Thus, imaging in the x- and y-directions can be affected separately.

In a particularly advantageous embodiment, the field mirror (s) are grazing incidence mirror (s). In EUV systems, the reflection loss for normal incident mirrors is much higher than for grazing incident mirrors. Thus, grazing incidence mirrors are preferred.

In an embodiment of the invention, the illumination system consists of optical components for delivering the light source to the auxiliary light source. This optical component can be a first mirror that is separated into a single mirror component. The mirror component generates one auxiliary light source. The mirror component may be provided as a planar, spherical, cylindrical, toroidal or aspheric surface. This single mirror component is called the field plane. They are burned in the image plane of the irradiation, and the image of the field surface is at least partially doubled.

For extending the light source or for other purposes, it is advantageous to add a second mirror which is divided into several single mirror components. Each mirror component is located in an auxiliary light source. This mirror component is called the pupil plane. The pupil plane typically has a positive optical power and images the corresponding field plane in the image plane.

The imaging of the field surface into the image plane can be divided into radial image formation and azimuth image formation. The y direction of the field surface may be imaged in the radial direction, and the x direction may be imaged in the azimuth direction of the arc-shaped field. To induce irradiation roughness perpendicular to the scanning direction, azimuth image formation will be aberration.

With the field lens, imaging of the field surface can be induced. Thus, it is advantageous to change the azimuth aberration by changing the surface parameter of the field lens.

The field lens is shaped such that the auxiliary light source generated by the field surface is imaged with a given exit pupil of the irradiation system.

With the static design of the field lens, a given distribution of irradiation illuminance, the shape of the irradiated field and pupil imaging can be realized. Known effects at the design stage can be considered as the design of the field lens. However, the effect is unpredictable. Coatings vary slightly between systems. This is the variation of illumination intensity and time dependent variable effect, ie setting dependent variable effect due to different coherence. Thus, in a very useful embodiment of this invention, an actuator on the field mirror (s) is provided to control the refractive surface.

The aberration and thereby the illumination roughness can be adjusted using an actuator. Since surface changes do not affect pupil imaging, roughness correction and pupil imaging can be considered simultaneously. The surface change is limited to the fact that the direction of the centerline in the image plane is changed to less than 5 mard, preferably less than 2 mrad, more preferably less than 1 mrad.

It is advantageous to reduce the number of surface parameters that are controlled. In order to derive irradiation illumination and scanning illumination, only these surface parameters can be adjusted to derive the shape of the mirror surface (s) perpendicular to the scanning direction. If the scanning direction is the y direction, they are x parameters.

Particularly simple arrangements are obtained when the actuators controlling the field mirror surface are laid in the form of a line or beam actuator parallel to the scan direction or the y axis of the field mirror.

Except for the irradiation system, the present invention can use a projection exposure system for microlithography having such an irradiation system. A mask or reticle will be arranged in the image plane of the illumination system, which is the interface between the illumination and the projection system. The mask will be imaged onto the wafer plane using the projection.

Irradiation of the wafer is typically transfer centric. This means that the angle of the principal line with respect to the wafer plane is less than ± 5 mrad. The angular distribution of the major lines in the reticle plane is given by the lens design of the projection. The direction of the centerline of the irradiation should be well suited to the direction of the main line of the projection system to obtain continuous line propagation. When the angular difference between the center line and the main line does not exceed a given angle in the plane of the reticle, for example ± 10.0 mrad, preferably ± 4.0 mrad, very preferably 1.0 mrad, the transmission center requirement is implemented in this invention. do.

For scanning lithography, it is very important that the scanning energy in the wafer plane is uniform. With the irradiation system described above, it is possible to achieve uniformity values of scanning energy in the wafer plane in the range of ± 7%, preferably ± 5% and more preferably ± 3%.

It can be seen how the magnification (β _s ) for the azimuth imaging of the field surface can be calculated for a given distribution of scanning energy. With a known azimuth magnification β _s , the design of the field lens can be made.

If the forecast distribution of scanning energy in the wafer plane is not obtained, the scanning energy can be corrected using the actuator of the field mirror (s). From the difference between the predicted and measured distribution of the scanning energy, the magnification and necessary surface correction for the azimuth imaging of the field surface can be calculated.

The invention will be fully understood from the following detailed description and the accompanying drawings which are not to be considered limiting of the invention. A broader scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, the detailed description and specific examples indicating certain embodiments of the present invention are merely illustrative, as changes and variations within the spirit of the present invention will become apparent to those skilled in the art from this detailed description. Given way.

1 illustrates a typical arc shaped field for an EUV irradiation system.

2 is a side view of a typical EUV irradiation system.

3 shows an image of the center plane in the plane of the reticle using the pupil plane and the field lens.

4 shows the conversion of rectangular fields in arc-shaped fields.

5 shows a calculated curve of the total scanning energy in the plane of the reticle taking into account the center field plane.

6 shows a simulated curve of total scanning energy in the plane of the reticle simulated as all field planes.

FIG. 7 shows the difference in the constellation of the arrow on the first field mirror without aberration correction and with aberration correction as variables of R _x , R _y , K _x , K _y ;

FIG. 8 shows the difference of the arrow on the second field mirror on the second field mirror without aberration correction and with aberration correction as a variable of R _x , R _y , K _x , K _y ;

9 shows the difference of the arrow on the first field mirror on the first field mirror without aberration correction and only with aberration correction as a variable of the conic constant K _x .

FIG. 10 shows the difference of the arrow on the second field mirror on the second field mirror without aberration correction and only with aberration correction as a variable of the conic constant K _x .

FIG. 11 shows the arrangement of actuators in top and side views for dynamic control of the surface formation of the second field mirror. FIG.

12 is a side view of a typical EUV projection exposure system.

The irradiation system according to the invention described below has made clear the segments of the ring field as shown in FIG. 1. The arc-shaped field 11 in the reticle plane is an object imaged to the wafer plane by the projection.

According to FIG. 1, the width of the arc-shaped field 11 is Δr and the average radius is R ₀ . The arc-shaped field extends over each range of 2 · α ₀ and 2 · s ₀ arcs.

Each α ₀ is defined from the y side to the field edge, and the length s ₀ of the arc is defined from the center of the field to the field edge along the arc at an average radius R ₀ .

It has been found that the scanning energy SE (x) at x is the line integration of the roughness E (x, y) along the scan direction, which is the y-axis direction of this embodiment. In other words,

SE (x) = And E (x, y) is the illuminance distribution in the xy plane.

Each point on the reticle or wafer includes a scanning energy SE (x) corresponding to its x coordinate. If uniform exposure is desired, it is advantageous for the scanning energy to be an independent variable of x. Uniform scanning energy distribution is typically a strong requirement in the wafer plane.

How scanning energy is controlled by the design of the field lens will be described later.

As an example, an EUV irradiation system is shown in FIG. 2. In this embodiment, the laser generating plasma source 200 can generate photons at λ = 13 nm. The light source is collected by the elliptical mirror 21 and directed to the first mirror 22, which is composed of several mirror elements. Single mirror elements are called field planes because of the fact that they are imaged in the image plane 26 of the illumination system. In this embodiment, the field surface is a planar mirror element, and each field surface is inclined by a large difference. An elliptical mirror 21 is designed to image the light source 200 in the aperture stop plane 23. Due to the inclined field surface, the image of the light source is divided into several auxiliary light sources 201. The number of auxiliary light sources 201 depends on the number of inclined field surfaces. The auxiliary light source 201 is imaged in the exit pupil 27 of the irradiation system using the field mirrors 24 and 25. The position of the exit pupil 27 depends on the design of the projection not shown in FIG. The field mirrors 24 and 25 are grazing incidence mirrors having a toroidal shape in this embodiment. The imaging of the field surface in the image plane 26 is affected by the field mirrors 24 and 25. They form an arc-shaped image of the rectangular field surface and introduce aberrations to control the irradiance in the reticle plane 26. This will be better explained below. The inclination angle of the field surface is selected to overlay an arc-shaped image of the field surface at least partially in the image plane 26.

The embodiment of FIG. 2 is only one example. The source is not limited to laser generated plasma sources. Lasers for wavelengths of 193 nm or less, light waves for wavelengths of 10 to 20 nm, pinch plasma sources, synchrotrons, or wiggers are also possible light sources. The collector unit is adapted to the angle and spatial characteristics of other light sources. The survey system is not purely projected.

3 is a schematic diagram of a three-dimensional space showing the imaging of one field surface 31 on the image plane 35. The beam path of this central field surface 31 located on the optical axis represents all other field surfaces. The incoming beam 300 is focused on the auxiliary light source 301 using the field surface 31. The field surface 31 is a concave mirror in this case. If a point source is used, the auxiliary light source 301 is like a spot. The beam branches back from the auxiliary light source 301. Without the field mirrors 33 and 34, the image of the rectangular field surface 31 can be rectangular. The image of the field surface 31 is aberration to obtain the arc-shaped field 302. Two mirrors are needed to get the right direction of the arc. The reflected beam 303 is concentrated at the exit pupil of the irradiation system using field mirrors 33 and 34. The exit pupil is not shown in FIG. Field mirrors 33 and 34 image the secondary light source 301 with the exit pupil.

For the actual source, the auxiliary light source 301 is extended. In order to obtain a sharp image of the field surface 31, it is advantageous to image the field surface 31 to the image plane 35 using another mirror 32. The mirror 932 located in the auxiliary light source 301 is called the pupil plane 32 and has a concave surface. A second mirror consisting of a single mirror is needed to extend the light source. The mirror with the pupil plane should be located in the plane of the auxiliary light source. In Fig. 2, the source diameter of the laser generating plasma source 200 is only 50 mu m, so that the pupil plane is missing. For larger source diameters, a mirror with pupil plane must be added at the aperture cooking plane 23. In order not to obtain any vignette light, the inclination angle of the mirror 22 having the field surface should be increased.

The field lenses 24, 25, 33, 34 in the embodiment shown in FIGS. 2 and 3 form an arc shaped field 302 and have an aperture stop 23 in the exit pupil plane 27 of the irradiation system. It images the plane of and controls the distribution of irradiation within the irradiated field 302.

The imaging of the central field surface 31 shown in FIG. 3 optimizes the design of the field mirrors 33 and 34. The shape of the image of the other field surface is determined by the field lens in almost the same manner with respect to the center field surface 31. Therefore, the design of the field lens that alternately controls the scanning energy can be optimized through the imaging of the central field surface 31. This side can be considered a homogeneous radiation side. In a practical system with all field faces, homogeneity results from the double print of all field faces.

4 is a diagram schematically showing the imaging of the rectangular field 41 on the arc-shaped field 42 in the image plane of the irradiation system. Rectangular field 41 may copy the real or imaginary plane homogeneously in a plane bonded to the reticle plane. In the embodiment of FIG. 2, rectangular field 41 is a central field plane that can be considered to represent all field planes.

The length x _w in the rectangular field 41 is imaged at the arc length s and the length y _w on the radial dimension r in the arc-shaped field 42. The origin of the coordinate system is the rectangular field 41 center of field and the arc-shaped field 42 optical axis.

When the field lens consists of a mirror (s) or lens (s), for example a toroidal mirror or a lens with distortion power, the image formation can be divided into two components β _s and β _r :

β _s : x _w → s

β _r : y _w → r

Here, the radial image of y _w on β _r ; r, β _s ; azimuth image of x _w on s, (x _w , y _w ); The horizontal and vertical coordinates of the field point on the rectangular field 41, and further include (s, r); The radius and azimuth coordinates of the field points on the arc-shaped field 42 are meant.

Assuming the homogeneous roughness distribution E _w (x, y) = E _w ⁰ , the influence of the field lens on the xy plane of the rectangular field, the illuminance distribution E _r (s, r) in the plane of the arc-shaped field 42 Is obtained by. The index w means below the plane of the rectangular field and the index r means below the plane of the arc-shaped field. If the azimuthal image formation β _s is free of aberrations, the illuminance distribution in the plane of the reticle is also uniform.

E _r (x, y) = E _r ⁰

Since the scan path is increased towards the edge of the field, the scanning energy SE (x _r ) in the plane of the reticle is a function of x _r ,

SE (x _r ) =

The following equation applies:

SE (x _r ) =

For Δr <R ₀ x _r <R ₀ , this equation can be expanded in a series of discrete Taylors after the first command:

The following parameters can be estimated for the arc-shaped field 42:

R ₀ = 100.0 mm

Δr = 6.0 mm; -3.0mm≤r≤3.0mm

α ₀ = 30。

As a uniform illuminance distribution E _r ^0, and scanning energy SE (x _r) is x = _r increases from the outer edges of the 50.0㎜ a _{SE (x r = 50.0㎜) =} 1.15 SE (x r = 0.0) = SE max.

Uniformity error occurs.

The maximum scanning energy SE _max is obtained at the field edge part (x _r = 50.0 mm) and the minimum scanning energy SE _min is obtained at the field (x _r = 0.0).

R ₀ = 200.0 mm

Δr = 6.0 mm; -3.0mm≤r≤3.0mm

With α ₀ = 14.5 _° , we obtain SE (x _r = 50.0 mm) = 1.03 SE (x _r = 0.0).

The uniformity error generated is as follows.

The increase in scanning energy towards the edge of the field is considerably smaller to be larger than the radius R ₀ of the arc-shaped field 42 and less than the arc angle α ₀ .

If the field lens is designed such that image formation in the plane of the reticle is aberrationally azimuth, that is, position dependent variable magnification If is introduced, uniformity can be substantially improved according to the present invention.

The illuminance of the irradiation E is defined as the quotient of dividing the radiation flux dΦ by the area dA calculated by the radiation flux. In other words

to be.

For arc-shaped fields, the cross-sectional area is

A = dsdr

Where ds is the increment of the arc and dr is the radial increment.

If azimuthal imaging is aberration, the aberration roughness in the reticle plane acts as an inverse of the quotient divided by the increment ds ^v of the aberration arc by the increment ds ^{v = 0} of the non-aberration arc.

Since the increment of the arc (dsv = 0) with non-aberration image formation is proportional to the x-increment in the rectangular field 41, i.e., ds ^{v = 0} dxdx _w , the illuminance is as follows.

Roughness in the plane of the reticle Is It can be controlled by changing the quotient.

The relationship between scanning energy SE (x _r ) and azimuthal image magnification β _s is inferred as follows:

The roughness E (x _n , y _r ) is recorded as the product of the functions g (r) and f (s) The function (g (r) is only dependent on the radial r and the function (f (s) is the azimuth angle It only depends on the scope:

E (x _n , y _r) = g (r) · f (s).

For Δr <R ₀ x _r <R ₀ , g (r) is an independent variable of x-position (x _r ) in the plane of the reticle and f (s) is independent of y-position (y _r ) in the plane of the reticle Variable.

Since s and x _r are directly paired with each other, SE (x _r ) can also be written as follows as a function of s.

Since f (s) is an independent variable of y _r ,

Also, Because

to be. Aberration The derivation of shows that it is proportional to the function f (s):

In other words, to be.

Is an independent variable of s,

to be.

Considering the combination of s and x _r , to be.

value From, the scanning energy can be set directly, with x _{r being} the x component of the field point on the arc-shaped field 42 and x _{w being} the x component of the field point on the rectangular field 41.

From a given curve of in-plane scanning energy SE (x _r ) and SE (s) of the reticle, the azimuth imaging magnification β _s can be calculated with this formula.

Edge of rectangular field 41 The constant c 'is obtained from the boundary conditions that are imaged on the edge of the arc-shaped field at.

s (x _w ) and thus the imaging magnification (β _s (x _w )) are subsequently known as a function of x _w . In other words,

The above equation for the azimuth magnification β _s is solved as an example for the constant scanning energy SE (x _r ) in the plane of the reticle.

For the constant in-plane scanning energy SE ⁰ of the reticle, the azimuthal imaging magnification is derived as follows:

Also, therefore

to be.

The investigation system will be considered as follows:

In-plane rectangular field 41 joined to the plane of the reticle:

-8.75 mm ≤ _{x w} ≤ 8.75 mm

-0.5 mm ≤ y _w ≤ 0.5 mm

In-plane arc-shaped field 42 of the reticle:

-52.5 mm ≤ s ≤ 52.5 mm

-3.0 mm≤r ≤3.9 mm

With a boundary condition of s (x _w = -8.75) = 52.5 mm, the constant c "is obtained as follows: c" = 954.983, and therefore, to be.

If the design of the field lens produces a curve of azimuth imaging magnification, a constant scanning energy is obtained in the plane of the system reticle defined by the example.

By changing the azimuth magnification β _s it is necessary to use in a lithographic system to take into account the fact that in addition to the field formation, the field lens determines the image or aperture stop plane of the second light source as the incident pupil of the projection. This does not allow for any large aberration correction as with geometric boundary conditions.

The uniformity correction described above is not limited to the irradiation system with the planar mirror described as an example, but can be generally used. By aberration the image in the reticle plane perpendicular to the scanning direction, the illuminance distribution and thus the scanning energy distribution can be controlled.

Typically, the irradiation system comprises a real or imaginary plane with a second light source. If you have a Kheler irradiation system, you always have this plane. The above-described real or imaginary plane is imaged in the incident pupil of the object using a field lens, and an arc-shaped field is generated in the pupil plane of this image. In this case, the pupil plane of the pupil imaging is the plane of the reticle.

Some examples of embodiments of the irradiation system in which the distribution of scanning energy is controlled by the design of the field lens are described below. The general arrangement of the irradiation system is shown in FIG. The optical data of the survey is summarized in Table 1.

Ref. In FIG. No. Surface Parameters (Radius R, Conical Constant K) Thickness along the optical axis d [mm] Bend angle of the optical axis α _x [。] Source 200 ∞ 100.000 0.0 Collector mirror 12 R = 183.277mmK = 0.6935 881.119 0.0 Mirror with field face 22 ∞ 200.000 7.3 Aperture aperture plane 23 ∞ 1710.194 0.0 1st field mirror 24 R _y = -7347.291 mm R _x = -275.237 K _y = -384.814 K _x = -3.813 200.000 -80.0 2nd field mirror 25 R _y = 14032.711mmR _x = 1067.988K _y = -25452.699K _x = -667.201 250.000 80.0 Reticle 26 ∞ 1927.420 2.97 Exit pupil 27 ∞

The irradiation system of FIG. 2 and Table 1 has a source diameter of 50 μm, which is optimized for the laser generated plasma source 200 at λ = 13. The solid angle (Ω) of the collected radiation is about 2π.

The mirror 22 having a field surface has a diameter of 70.0 mm, and the planar field surface has a rectangular shape having an xy dimension of 17.5 mm × 1.0 mm. The mirror 22 consists of the field surface 220. Each side is inclined with respect to the x- and y-axes to at least partially overlay the image of the field side in the image plane 26. At the edge of the mirror 22, the field surface has the largest inclination angle of about 6 °. The mirror 22 was inclined to an angle α _× = 7.3 ° in order to bend the optical axis at 14.6 °.

The aperture stop plane 23 is not acceptable in this example.

The first and second field mirrors 24 and 25 are flat projection mirrors. Each of them bends the optical axis up to 160 °. The field mirror 24 is a concave mirror, and the mirror 25 is a convex mirror. They are optimally used to control illumination intensity, field shape, and pupil image. In the examples below, only these two mirrors can be exchanged. Their position and inclination angle are always the same. It will be appreciated that by changing the surface shape, it is possible to change the illuminance distribution while the pupil image and the field shape are kept within error tolerance.

The in-plane arc-shaped field of the reticle 26 can be described as follows.

R ₀ = 100.0 mm

Δr = 6.0 mm; -3.0mm≤r≤3.0mm

α ₀ = 30。

The reticle 26 is inclined to α _x = 2.97 ° with respect to the optical axis.

The position of the exit pupil 27 of the irradiation system is defined by the given design of the projection object.

A particular aspect of the present invention consists in describing the aspherical surface of the mirror surface, which on the one hand provides good uniformity of scanning energy and, on the other hand, good telecentricity. The aspheric surface of the mirror surface can be varied, while the tilt angle and spacing of the mirror remains constant.

Listed examples of examples will appear and be compared with reference to the following pantomers.

SE _max : Maximum scanning energy in the irradiated field.

SE _min : Minimum scanning energy in the irradiated field.

Maximum transmission center error Δi _max across the field investigated in the reticle plane:

Δi _max = [i _act -i _ref ] _max , unit: [mrad]

i _act : Central beam angle with respect to the plane of the reticle at the field point.

i _ref : The major beam angle of the projection relative to the plane of the reticle at the field point.

The maximum transmission center error (Δi _max ) will be calculated for each field point in the field examined. The direction of the principal ray of the in-plane projection of the reticle only depends on the design of the projection. Typically the main beam hits the wafer plane transmissionally.

To obtain the transmission center error in the wafer plane, the transmission center error in the reticle plane is divided by the magnification of the projection. Typically, the projection is a reduction with a magnification of β = 0.25. The transmission center error in the wedge plane is four times the transmission center error in the reticle plane.

Geometrical parameters of the first field mirror: R _x , R _y K _x , K _y

Geometrical parameters of the second field mirror: R _x , R _y K _x , K _y

Both field mirrors are toroidal mirrors with surface parameters defined in the x- and y- directions. R is the radius and K is the conical constant. It can also change higher than the aspheric constant. However, in one example of the embodiment, only the radius and conical constant will change.

First embodiment

For field lenses having pure spherical x and y cross sections, the following characteristics are obtained.

-Uniformity = 10.7%

Δi _max = 0.24 mrad

Field mirror 1: R _x = -290.18, R _y = -8391.89, K _x = 0.0, K _y = 0.0

Field mirror 2: R _x = -1494.60, R _y = -24635.09, K _x = 0.0, K _y = 0.0

The curve of the scanning energy in the in-plane x direction of the reticle is plotted in FIG. 5 as a solid line 51. Because the system is symmetric about the y axis, only the curved anodes are shown. Scanning energy is 100% normalized at the center of the field. Scanning energy rises to the edge of the field at 124%. The calculation is considered to be just an image of one representative field plane, in this case the center field plane, which is assumed to be a uniform radiation plane.

However, this relationship can also be maintained for the entire system as shown as a result for the overall field plane of FIG. 6. The curve of FIG. 6 is the result of a simulation with the entire irradiation system and laser generated plasma source 200 according to FIG. 2. The solid line 61 means the scanning energy for the toroidal field mirror of the first embodiment without the conical constant.

By comparing the curves, it can be clearly seen that the results of FIGS. 5 and 6 are contrasting, and the following approximation is the result of considering various things.

Reduction of the problem of image of rectangular face, in this case the center field face.

Δr <R: Discontinuity of the Taylor series after the first command.

A system will be described below that includes a toroidal field mirror in which the koenic constants are changed and the field mirrors are post optimized as their tilt angles and positions are retained.

Second embodiment

Uniformity = 2.7%

Δi _max = 1.77 mrad

Field mirror 1: R _x = -275.24, R _y = -7347.29, K _x = -3.813, K _y = -385.81

Field mirror 2: R _x = 1067.99, R _y = 14032.72, K _x = -667.20, K _y = -25452.70

Dotted line 52 in FIG. 5 shows the curve of scanning energy expected from the design for the center field plane; The curve scanning energy obtained with the entire system of all field faces is shown by dashed line 62 in FIG. 6. Improvements in scanning uniformity are evident using conical constants in the design of field mirrors.

The necessary surface corrections on the two field mirrors 24 and 25 are shown in contour lines in FIGS. 7 and 8. The mirror is bounded according to the depicted area on the mirror. Border lines are indicated by 71 and 72. The contour lines show the difference in the constellations of the surfaces of the first and second embodiments in millimeters.

For the first field mirror 24, the largest arrow difference is in the order of grade of 0.4 mm in FIG. This is also the signal inversion of the arrow difference.

For the second field mirror 25, the largest arrow difference is in the rank order of 0.1 mm in FIG. 8.

The second embodiment is utilized to the maximum to obtain an optimal improvement in scanning uniformity to accommodate transmission center errors. Transmission center disturbance of 1.77 mrad in the reticle plane of the second embodiment is a problem for the lithographic system.

The example below is chosen such that the maximum in-plane transmission center disturbance of the reticle is 1.0 mrad or less.

The starting point for the design of the field mirror in the following example is the design of the example of Example 1. In each example, other settings of the surface parameters are freely set.

Third embodiment

Free parameters R _x ^{first mirror} , R _y ^{first mirror} , K _x ^{first mirror} , K _y ^{first mirror} , R _x ^{second mirror} , R _y ^{second mirror} , K _x ^{second mirror} , K _y ^{second mirror} .

Uniformity = 4.6%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -282.72, R _y = -7691.08, K _x = -2.754, K _y = -474.838

Field mirror 2: R _x = 1253.83, R _y = 16826.99, K _x = -572.635, K _y = -32783.857

Fourth embodiment

Free parameters R _x ^{first mirror} , K _x ^{first mirror} , K _y ^{first mirror} , R _x ^{second mirror} , K _x ^{second mirror} , K _y ^{second mirror} .

Uniformity = 5.1%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -285.23, R _y = -8391.89, K _x = -2.426, K _y = -385.801

Field mirror 2: R _x = 1324.42, R _y = 24635.09, K _x = -568.266, K _y = -31621.360

Fifth Embodiment

Free parameters R _x ^{first mirror} , K _x ^{first mirror} , R _x ^{second mirror} , K _x ^{second mirror} .

Uniformity = 5.1%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -280.08, R _y = -8391.89, K _x = -2.350, K _y = 0.0

Field mirror 2: R _x = 1181.53, R _y = 24635.09, K _x = -475.26, K _y = 0.0

Sixth embodiment

Free parameters K _x ^{first mirror} , K _y ^{first mirror} , K _x ^{second mirror} , K _y ^{second mirror} .

Uniformity = 6.0%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -290.18, R _y = -8391.89, K _x = -2.069, K _y = -290.182

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = -503.171, K _y = -1494.602

Seventh embodiment

Free parameters K _x ^{first mirror} , K _x ^{second mirror} .

-Uniformity = 7.0%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -290.18, R _y = -8391.89, K _x = -1.137, K _y = 0.0

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = -305.384, K _y = 0.0

Eighth embodiment

Free parameters R _x ^{first mirror} , R _y ^{first mirror} , K _x ^{first mirror} , K _y ^{first mirror} .

Uniformity = 7.8%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -288.65, R _y = -8466.58, K _x = -0.566, K _y = 139.337

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = 0.0, K _y = 0.0

9th embodiment

Free parameters R _x ^{first mirror} , K _x ^{first mirror} , K _y ^{first mirror} .

Uniformity = 7.8%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -288.59, R _y = -8391.89, K _x = -0.580, K _y = 111.346

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = 0.0, K _y = 0.0

10th embodiment

Free parameters R _x ^{first mirror} , K _x ^{first mirror} .

Uniformity = 8.1%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -288.45, R _y = -8391.89, K _x = -0.574, K _y = 0.0

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = 0.0, K _y = 0.0

Eleventh embodiment

Free parameters K _x ^{first mirror} , K _y ^{first mirror} .

-Uniformity = 8.5%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -290.18, R _y = -8391.89, K _x = -0.304, K _y = -290.182

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = 0.0, K _y = 0.0

12th embodiment

Free parameters K _x ^{First mirror} .

-Uniformity = 8.6%

Δi _max = 1.00 mrad

Field mirror 1: R _x = -290.18, R _y = -8391.89, K _x = -0.367, K _y = 0.0

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = 0.0, K _y = 0.0

Various examples of embodiments will be summarized in Table 2 where the free parameters are indicated horizontally.

R _x ^{1st mirror} R _y ^{first mirror} K _x ^{1st mirror} K _y ^{first mirror} R _x ^{2nd mirror} R _y ^{2nd mirror} K _x ^{2nd mirror} K _y ^{second mirror} Uniformity [%] In-plane transmission center errorΔi _max [mrad] No conic constant 10.7 0.24 Change, field mirror 1 × 8.6 1.0 × × 8.5 1.0 × × 8.1 1.0 × × × 7.8 1.0 × × × × 7.8 1.0 Change, field mirror 1 + 2 × × 7.0 1.0 × × × × 6.0 1.0 × × × × 5.1 1.0 × × × × × × 5.1 1.0 × × × × × × × × 4.6 1.0

Table 2 shows that field mirror 1 and field mirror 2 improve scanning uniformity to approximately the same range with the base fraction done by the x parameter that ultimately determines the azimuth magnification scale (β ₈ ).

Although only static correction of uniformity has been investigated so far as an example of essentially "skewed" embodiments, the active variant of the present invention will be described below. In this case the actuation can be generated by a mechanical actuator. Possible actuators may be piezo-elements at the back of the field mirror to change the shape of the mirror by changing the voltage to the piezo-elements. As discussed above, large improvements in uniformity can occur even when only the x plane parameter is changed. If the koenic constant changes in the x direction, the arrow difference has the same logarithmic signal that favors surface manipulation over the entire surface. 9 and 10 show the difference in the constellations between Example 6 and Example 1. FIG. The conic constant in the x direction is changed for the field mirrors 1 and 2. The maximum arrow difference is 250 μm for the first field mirror 24 and 100 μm for the second field mirror 25. Uniformity is improved from 10.7% to 7.0% with an additional transmission center disturbance of 1.0mard at the reticle surface. This transmission center disturbance corresponds to 4.0 mard in the plane of the wafer if the projection has a magnification of β = -0.25. Thus, the uniformity of the scanning energy can be corrected up to ± 3.7% by the active magnification of the field lens.

When the koenic constant changes in the x direction, the arrow sign changes only with x. The line with the same arrow difference is almost parallel to the y axis in the scanning direction.

The arrow position distribution (pfh _ref ) of the reference surface (first embodiment) of the field mirror can be described as follows.

x and y are mirror coordinates in the local coordinate system of the mirror surface. R _x and R _y are the radius of the cooidal mirror.

The arrow position distribution (pfh _act ) of the operating surface of the field mirror is as follows.

K _x and K _y are conical constants. This is given for the arrow difference Δpfh.

Δpfh (x, y) = pfh _act (x, y) -pfh _ref (x, y)

In Example 1:

Field mirror 1: R _x = -290.18, R _y = -8391.89, K _x = 0.0, K _y = 0.0

Field mirror 2: R _x = -1494.60, R _y = 24635.09, K _x = 0.0, K _y = 0.0

In Example 6:

Field mirror 1: R _x = -290.18, R _y = -8391.89, K _x = -1.137, K _y = 0.0

Field mirror 2: R _x = 1494.60, R _y = 24635.09, K _x = -305.384, K _y = 0.0

It is essentially desirable for the actuator or mechanical regulator to be placed on equipotential lines 92, 102 (positions of the same arrow difference). This row of identical actuators operates almost parallel to the y axis in Example 6 described so far. Thus, while such an embodiment is not necessary to control the two-dimensional field of the actuator, it is sufficient to merely control the rows of the other actuator banks.

For example, on the second field mirror image, an arrangement of actuator rows may be proposed as shown in FIG. 11. The second field mirror is shown in a top view (x-y-degree) in front view and side view (x-z-degree) at the bottom of FIG. 11. In the plan view, the actuator beams 5 ', 4', 3 ', 2', 1 ', 0, 1, 2, 3, 4, 5 are arranged along the equipotential lines. Since they are symmetric about the y axis, the corresponding actuator beams 5 and 5 ', or 4 and 4', or 3 and 3 ', or 2 and 2', or 1 and 1 'can be activated with the same signal. The actuators in the top view are shown by lines and in the side views by arrows.

An industrial tool allows the entire row of actuators to be designed as actuator beams 5 ', 4', 3 ', 2', 1 ', 0, 1, 2, 3, 4, 5. When the beam is actuated, the entire heat of the actuator is raised or lowered.

The distance between the actuator beams can be selected depending on the gradient of the arrow difference. For high values of the gradient, a dense array of actuator beams is required, and for low values of the gradient the distance must be increased. In the example of FIG. 10, the gradient of the arrow is higher at the edge of the irradiation field because the actuator beam is more at the edge of the field than at the center as shown in FIG. 11.

Activity correction of uniformity can be performed using the above-described actuator as follows.

In-plane scanning energy SE _standard (Xr) of the reticle was established based on the geometric design of the field lens.

In-plane scanning energy SE _w (X _w ) of the wafer is measured including the coating, absorption, and vignetting effects.

For lithographic processes, SE _w (X _w ) must be independent of the in-plane x-position (x _w ) of the wafer. If this is not the case, the x _w -dependent offset must be addressed by the survey system.

Since the image of the reticle plane on the wafer plane is almost an image, SE _w (X _w ) can be converted directly to the reticle plane SE _w (X _r ) using a given magnification of the projection.

If the design reference SE _standard (X _r ) and the measured distribution (SE _w (X _r )) are normalized to 100% dpj for x _r = 0.0, the necessary correction of the field mirror is the difference ( Can be calculated from

= SE _w (x _r ) -SE _standard (x _r )

( ) Determines the azimuth magnification β _δ .

If, for example, this is due to the effect of time dependent or survey setting dependent variables, the difference between the target (SE _standard (x _r )) and the actual value (SE _w (x _r )) ( ), The uniformity of the scanning energy can be corrected by the above-described actuators within certain limits. Up to ± 2.5% uniformity can be corrected with one operable field mirror, and up to ± 5.0% can be corrected with two operable field mirrors.

In the case of electrostatic variation, for example in the case of deviations from coating effects, absorption effects known in the design, etc., this effect is considered a modified field lens design, and correction as an actuator is then unnecessary.

Illuminance lossless control of scanning energy is achieved during the first time period by the present invention, and field dependent variable scan paths, coatings, absorption, and vignetting are achieved if considered a static design of the field lens. The present invention also proposes dynamic control as an active field mirror for time dependent or irradiation setting dependent variable effects. If a transmission center error of ± 4.0 mrad is allowed in the plane of the wafer, uniformity correction can be up to ± 5%.

In Fig. 12, a laser generating plasma source as the light source 120, an irradiation system 121 corresponding to the present invention, a mask 122 called a reticle, a positioning system 123, a projection 124, and a wafer ( A projection exposure system consisting of 125 is shown to be exposed on the position table 126. Projection 124 for EUV lithography is a mirror system having an even mirror to have a wafer and a reticle on the other side of the projection 124.

Detection units in the reticle plane 128 and the wafer plane 129 are provided for measuring the illuminance distribution inside the irradiation field. The measurement data is sent to the counting unit 127. Scanning energy and scanning uniformity can be evaluated with the measurement data. If there is a difference between the predetermined roughness distribution and the measured value, the surface correction is calculated. In one field mirror the actuator drive 130 is braked to manipulate the mirror surface.

The present invention is not limited to irradiation systems with laser generated plasma sources. Irradiation systems for synchrotrons, wiggler, undulator or pinch-plasma sources are known from patent application DE 99106348.8 (US series no. 09/305017) or PCT / de99 / 02999. The irradiation system shown in this application comprises a field mirror as described above. The idea of correcting uniformity by introducing vertical aberrations in the scanning direction can be applied directly to such survey systems.

FIELD OF THE INVENTION The present invention relates to an irradiation apparatus for slit irradiation for scanning lithography, in particular EUV lithography, having a wavelength of 193 nm or less, in which a field mirror (s) or field lens (s) are formed in the irradiation apparatus, so that the irradiated field is scanned. It has the effect of aberration in the reticle plane perpendicular to the direction.

Claims (30)

Irradiation apparatus for slit irradiation for scanning lithography, in particular EUV lithography, having a wavelength of 193 nm or less, Light Source, One or more field mirrors or one field lens, and And the field mirror (s) or field lens (s) are shaped so that the irradiated field is aberration in the image plane perpendicular to the scanning direction. 2. The irradiation of claim 1, wherein the field mirror (s) or field lens (s) are shaped such that a constant illuminance distribution of the irradiated field is achieved using field mirror (s) or field lens (s). Device. 3. An irradiation apparatus according to claim 1 or 2, wherein the illuminance in the irradiated field varies along a direction perpendicular to the scanning direction. 4. The irradiation apparatus of claim 3, wherein the illuminance is reduced from the center of the field to the field edge portion. 4. The irradiation apparatus of claim 3, wherein the irradiation illuminance increases from the center of the field to the field edge portion. 6. An irradiation apparatus according to any one of claims 1 to 5, wherein the uniformity of the scanning energy on the image plane is in the range of ± 7%, preferably ± 5%, and very preferably ± 3%. 7. The irradiator according to any one of claims 1 to 6, wherein the irradiator comprises an aperture diaphragm, wherein the field mirror (s) or field lens (s) are arranged within a constant exit cavity of the irradiator. Irradiation apparatus characterized in that it is molded to be imaged. The field mirror (s) or field lens (s) of claim 1, wherein the constant shape of the irradiated field is achieved using the field mirror (s) or field lens (s). Irradiation apparatus, characterized in that molded to be. 9. Apparatus according to any one of the preceding claims, wherein the irradiated field is a segment of a rectangular or ring field. 10. The irradiation apparatus according to any one of claims 1 to 9, wherein the field lens (s) or field mirror (s) are of a toroidal structure. 11. Apparatus according to any one of the preceding claims, wherein the field mirror (s) are grazing incidence mirror (s). 12. Apparatus according to any one of the preceding claims, wherein an optical component is provided for converting the light source into an auxiliary light source. 13. An irradiation apparatus according to claim 12, wherein said switching optical component has a first mirror divided into several single mirror components. 14. An irradiating apparatus according to claim 13, wherein the mirror component of said first mirror is field surfaces, said field surfaces being imaged as an image plane. 15. The irradiation apparatus according to any one of claims 12 to 14, wherein said irradiation apparatus has a second mirror divided into several single mirror components, said mirror components being located in an auxiliary light source. 16. An irradiation apparatus according to claim 15, wherein the mirror component of the second mirror is a pupil plane and the field plane is imaged onto the image plane using the pupil plane and field mirror (s) or field lens (s). . 17. The method according to any one of claims 14 to 16, wherein the imaging of the field surface onto the image plane can be divided into radial imaging and azimuth imaging, wherein the azimuth imaging is aberration. Irradiation device. 18. The field mirror (s) or field lens (s) of claim 17, wherein the field mirror (s) or field lens (s) are shaped such that a constant azimuth aberration of the image formation of the field surface is achieved using the field mirror (s) or field lens (s). Irradiation device. 19. The irradiation apparatus according to any one of claims 12 to 18, wherein the field mirror (s) or field lens (s) are shaped such that an auxiliary light source is imaged at a constant exit pupil of the irradiation apparatus. 20. The irradiation apparatus according to any one of the preceding claims, wherein the field mirror (s) comprise an actuator for active control of the mirror surface (s). 21. An irradiation apparatus according to claim 20, wherein said aberration and thus roughness distribution are adjusted in the field irradiated using an actuator. 22. Irradiation according to claim 20 or 21, characterized in that if the mirror surface (s) is adjusted, the direction of the centerline in the image plane is changed to less than 5 mrad, preferably less than 2 mrad, more preferably less than 1 mrad. Device. 23. The irradiation apparatus according to claim 21 or 22, wherein the change in aberration is made by adjusting only this surface parameter of the field mirror (s) that affects the shape of the surface (s) perpendicular to the scanning direction. . The irradiation apparatus according to any one of claims 20 to 23, wherein the actuators are arranged in rows parallel to the scanning direction. Mask on support system, A projection for imaging the mask on an image plane, and A projection exposure apparatus for scanning-microlithography having a photosensitive object on a support system in an image plane of the projection, the projection exposure apparatus comprising an irradiation apparatus according to any one of claims 1 to 24, wherein the mask is A projection exposure apparatus, characterized in that located on the image surface of the irradiation apparatus. 26. A projection exposure apparatus according to claim 25, wherein the maximum deviation between the main line and the centerline direction of the projection on the mask surface is ± 10.0 mrad, preferably ± 4.0 mrad, more preferably ± 1.0 mrad. 27. A projection exposure apparatus according to claim 25 or 26, wherein the uniformity of the scanning energy in the image plane of the projection is in the range of ± 7%, preferably ± 5%, and more preferably ± 3%. A static correction method of scanning energy in a projection exposure apparatus according to any one of claims 25 to 27, Providing a slit to be irradiated with a scanning energy of a predetermined distribution, Calculating a curve of magnification β _s of the azimuth angle to achieve a predetermined distribution of scanning energy, and Determining the shape of the field mirror (s) or field lens (s) to achieve a calculated curve of the azimuth magnification β _S. A dynamic correction method of scanning energy in a projection device according to any one of claims 25 to 27, Measuring the distribution of scanning energy (SE _w (X _w )) at the wafer surface, Comparing the measured curve SE _w (X _w ) of the measured scanning energy with a predetermined scanning energy distribution SE _STANDARD (X _w ), and If there is a difference, the appropriate actuator of the field mirror (s) is actuated until the measured distribution of scanning energy SE _w (X _w ) corresponds to the predetermined scanning energy distribution SE _STANDARD (X _w ). And a step in which a predetermined uniformity is achieved. 30. A method of manufacturing a microstructured device by a lithographic method using a projection exposure apparatus according to any one of claims 25 to 29.